YongHyun Cho

This study evaluates the charring behaviour of cross-laminated timber (CLT) wall panels manufactured from Korean larch (Larix kaempferi) and compares the experimentally determined charring rates with predictions from four fire design standards: KDS 41 50 50 (Korea, 2026 draft), EN 1995-1-2:2004 (Eurocode 5), prEN 1995-1-2:2025 (draft Eurocode 5), and AWC FDS 2024 (United States). Three CLT wall specimens were tested under non-load bearing, single-sided ISO 834 standard fire conditions: one 5-ply specimen (900 × 900 mm, 150 mm thick, unprotected) and one 3-ply specimen (900 × 900 mm, 90 mm thick, protected with 12.5 mm gypsum plasterboard), both bonded with a heat-resistant epoxy adhesive exposed for 120 min (one unprotected, one protected with 12.5 mm gypsum plasterboard), and one 4-ply specimen (112 mm thick) bonded with a two-component polyurethane (2c-PUR) adhesive exposed for 90 min. The experimental data were supplemented with published results from two additional Korean larch CLT test programs employing phenol-resorcinol formaldehyde (PRF) and one-component polyurethane (1c-PUR) adhesives, respectively. Three distinct adhesive performance groups were identified. Heat-resistant adhesives (heat-resistant epoxy and PRF) yielded cumulative charring rates of 0.50–0.67 mm/min, the 2c-PUR specimen yielded 0.84 mm/min, and the 1c-PUR specimen yielded 0.94 mm/min, approximately 1.3–1.7 and 1.4–1.9 times higher than the heat-resistant group, respectively. The AWC FDS nonlinear charring model for bond-line-intact CLT showed the closest agreement with heat-resistant adhesive data (within ±20%), while the prEN 2025 phase-based model with k3 = 1.3 for vertical walls best captured 1c-PUR adhesive behavior. The findings demonstrate that adhesive type is the dominant factor governing CLT charring rate, with the observed three-group classification providing an experimentally grounded framework for differentiating charring provisions by bond line performance in fire design standards.

Recently, studies have been carried out to apply lean duplex stainless steels, with less than 1.5% nickel, which provides higher material strength and lower cost compared with austenitic stainless steel for building structures. This study compared with existing experimental and finite element analysis results on the structural behaviours of cold-formed lean duplex stainless steel welded connections with different tensile strength (tensile strength-to-yield stress ratio) and plate thickness despite identical steel grade. The main variables are plate thickness and weld lengths. The material tensile strength of a 3.0 mm thick plate was 22% lower than that of a 1.5 mm thick plate. All specimens showed block shear facture in the base metal. Block shear strengths predicted by current design codes and the proposed equations from previous studies were compared with test strengths. KDS 41 31 00-19/AISC2016 and EC3 design specifications underestimated block shear capacity by on average 24%, 43%, respectively for 1.5 mm and 3.0 mm thick specimens, and equations suggested in previous studies of stainless steel welded connections did not sufficiently account for the influence of stress triaxiality by material property and plate thickness difference on the block shear strength of lean duplex stainless steel specimens. Therefore, thickness-dependent modified strength equations were recommended based on experimental and numerical studies of lean duplex stainless steel welded connections and comparison of carbon steel and other stainless steel connections.

Composite solid electrolytes (CSEs) are newly emerging components for all‐solid‐state Li‐metal batteries owing to their excellent processability and compatibility with the electrodes. Moreover, the ionic conductivity of the CSEs is one order of magnitude higher than the solid polymer electrolytes (SPEs) by incorporation of inorganic fillers into SPEs. However, their advancement has come to a standstill owing to unclear Li‐ion conduction mechanism and pathway. Herein, the dominating effect of the oxygen vacancy (O_vac) in the inorganic filler on the ionic conductivity of CSEs is demonstrated via Li‐ion‐conducting percolation network model. Based on density functional theory, indium tin oxide nanoparticles (ITO NPs) are selected as inorganic filler to determine the effect of O_vac on the ionic conductivity of the CSEs. Owing to the fast Li‐ion conduction through the O_vac inducing percolation network on ITO NP–polymer interface, LiFePO₄/CSE/Li cells using CSEs exhibit a remarkable capacity in long‐term cycling (154 mAh g⁻¹ at 0.5C after 700 cycles). Moreover, by modifying the O_vac concentration of ITO NPs via UV‐ozone oxygen‐vacancy modification, the ionic conductivity dependence of the CSEs on the surface O_vac from the inorganic filler is directly verified.